The IRA admitted to the Dublin killing in 2013 during a meeting with the Stack family that was arranged by Mr Adams.

Last night, under questioning from RTE broadcaster Bryan Dobson, the Sin Fein leader eventually pledged to do everything he could "humanly do" to help the relatives of the slain prison officer.

He said everyone needed to "move forward" from the violence of the past - a remark that was strongly criticised by the victim's son, Austin.

"My family were tonight re-victimised by Gerry Adams as he tried to belittle our suffering," Mr Stack said.

"We are not vengeful people. My family just want the truth. Is that too much to ask?

"We want Sinn Fein to come clean about those in their ranks who sanctioned and planned my dad's murder.

"The public deserves full disclosure from Sinn Fein on this matter before the election."

The embarrassing episode came after the party's finance spokesman, Pearse Doherty, revealed his ambitions to succeed Mr Adams as party leader.

Mr Doherty has previously said he was not interested in the position.

His admission - just days before the general election in the Republic - is certain to come as a surprise to Mr Adams and senior Sinn Fein figures.

"In terms of whether I see myself in the future as a party leader, it's not something I have a personal ambition to do, but if it's something that the party so decided at a later stage that it was something they wanted me to do then I would be willing to do," he said.

The finance spokesman was also forced to defend his party leader's grasp of their tax policy following a "car crash" interview on RTE.

Mr Adams floundered as he came under intense questioning over Sinn Fein's controversial plans for a new higher rate of tax on salaries above €100,000.